Writing Device Drivers

I/O Control Support for 64-Bit Capable Device Drivers

The Solaris kernel runs in 64-bit mode on suitable hardware, supporting both 32-bit applications and 64-bit applications. A 64-bit device driver is required to support I/O control commands from programs of both sizes. The difference between a 32-bit program and a 64-bit program is the C language type model. A 32-bit program is ILP32, and a 64-bit program is LP64. See Appendix C, Making a Device Driver 64-Bit Ready for information on C data type models.

If data that flows between programs and the kernel is not identical in format, the driver must be able to handle the model mismatch. Handling a model mismatch requires making appropriate adjustments to the data.

To determine whether a model mismatch exists, the ioctl(9E) mode parameter passes the data model bits to the driver. As Example 15–14 shows, the mode parameter is then passed to ddi_model_convert_from(9F) to determine whether any model conversion is necessary.

A flag subfield of the mode argument is used to pass the data model to the ioctl(9E) routine. The flag is set to one of the following:

FNATIVE is conditionally defined to match the data model of the kernel implementation. The FMODELS mask should be used to extract the flag from the mode argument. The driver can then examine the data model explicitly to determine how to copy the application data structure.

The DDI function ddi_model_convert_from(9F) is a convenience routine that can assist some drivers with their ioctl() calls. The function takes the data type model of the user application as an argument and returns one of the following values:

DDI_MODEL_NONE is returned if no data conversion is necessary, as occurs when the application and driver have the same data model. DDI_MODEL_ILP32 is returned to a driver that is compiled to the LP64 model and that communicates with a 32-bit application.

In the following example, the driver copies a data structure that contains a user address. The data structure changes size from ILP32 to LP64. Accordingly, the 64-bit driver uses a 32-bit version of the structure when communicating with a 32-bit application.

Example 15–14 ioctl(9E) Routine to Support 32-bit Applications and 64-bit Applications

struct args32 {
    uint32_t    addr;    /* 32-bit address in LP64 */
    int     len;
struct args {
    caddr_t     addr;    /* 64-bit address in LP64 */
    int     len;

static int
xxioctl(dev_t dev, int cmd, intptr_t arg, int mode,
    cred_t *credp, int *rvalp)
    struct  xxstate  *xsp;
    struct  args     a;
    xsp = ddi_get_soft_state(statep, getminor(dev));
    if (xsp == NULL) {
        return (ENXIO);
    switch (cmd) {
    case XX_COPYIN_DATA:
        switch(ddi_model_convert_from(mode)) {
        case DDI_MODEL_ILP32:
            struct args32 a32;

            /* copy 32-bit args data shape */
            if (ddi_copyin((void *)arg, &a32,
                sizeof (struct args32), mode) != 0) {
                return (EFAULT);
            /* convert 32-bit to 64-bit args data shape */
            a.addr = a32.addr;
            a.len = a32.len;
        case DDI_MODEL_NONE:
            /* application and driver have same data model. */
            if (ddi_copyin((void *)arg, &a, sizeof (struct args),
                mode) != 0) {
                return (EFAULT);
        /* continue using data shape in native driver data model. */

        /* copyout handling */
        /* generic "ioctl unknown" error */
        return (ENOTTY);
    return (0);